A metallocene complex refers to a compound wherein a central metal coordinates to one or more cyclopentadienyl groups or derivatives thereof, and plays a very important role in various polymerization reactions as a catalyst. Here, a metal complex in combination with one cyclopentadienyl group or one derivative becomes a mono-metallocene complex. As a result of different types of central metals, metallocene complexes have completely different properties, such as catalyst activities for polymerization reaction. Particularly, after organic borane B(C6F5)3 and organic boron salts [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4] are successfully prepared and are used as efficient activating agents, mono-metallocene rare earth organic complexes exhibit superior activity and selectivity of polymerization in terms of catalysis of polymerization of polar and non-polar monomers (such as conjugated dienes, styrene, ethylene, α-olefins, or the like).
Metallocene complexes containing Group III metals or lanthanide metals have been reported as follows. In 1999, a mono-yttrocene dialkyl complex (C5Me4SiMe2R)Y(CH2SiMe3)2(THF) reported by German scientists, the group of Okuda, was milestone breakthrough (K. C. Hultzsch, T. P. Spaniol and J. Okuda, Angew. Chem. Int. Ed, 1999, 38, 227), and it exhibited high activity of olefin polymerization for the first time. The study group of Hou in Japan used a kind of mono-metallocene dialkyl rare earth metal complexes (C5Me4SiMe3)Sc(CH2SiMe3)2(THF), which may induce high-syndiotactic selective polymerization of styrene and high-active and high-stereoselective copolymerization of ethylene with styrene under the activation of an organic boron salt [Ph3C][B(C6F5)4] (Y. Luo, J. Baldamus and Z. Hou, J. Am. Chem. Soc., 2004, 126, 13910; US2007/0232758A1), and recently they successfully achieved binary copolymerization of styrene with 1,6-heptadiene or 1,5-hexadiene, ternary copolymerization of styrene and ethylene with 1,6-heptadiene or 1,5-hexadiene, and copolymerization of a cycloalkene (DCPD, norbornene) with 1-hexene by using a catalytic system of a benzylalkyl complex (C5Me4SiMe3)Sc(CH2C6H4NMe2-o)2/[Ph3C][B(C6F5)4] (F. Guo, M. Nishiura, H. Koshino and Z. Hou, Macromolecules 2011, 44, 2400; F. Guo, M. Nishiura, H. Koshino and Z. Hou, Macromolecules 2011, 44, 6335).
Cycloalkene polymers are expected to be used in optical materials instead of PMMA and PC due to their excellent heat resistance, strength, and optical properties. The major part in the petroleum cracking product C5-fraction is cyclopentadiene, which may spontaneously undergo Diels-Alder reaction at room temperature to be converted to DCPD. Therefore, the studies on copolymerization reactions of DCPD with ethylene, α-olefins, or styrene have been widely focused on. In recent years, with respect to catalysts for polymerization of ethylene with DCPD, ones which have been much studied are Ti and Zr complexes. However, DCPD has two active double bonds, wherein the activity of the carbon double bond at 5 and 6 positions is higher the carbon double bond at 2 and 3 positions, and when a copolymerization reaction of DCPD with an ethylene type monomer is performed using Ti and Zr polymerization catalysts, a crosslinked polymer is easily available (Naga, N. J. Polym. Sci., Part A: Polym. Chem. 2005, 43, 1285-1291) or the molecular weight of the copolymer and the content of DCPD are both relatively low. Transition metal compounds having heterocyclic ring fused 5-membered ring π ligands and olefin polymerization reaction using these transition metal compounds have been studied, and their catalytic advantages are high activity, high molecular weight, and so on. However, these transition metal complexes all contain side chains, mono-metallocene complexes without side chains having larger opening space have not been reported yet.